The present invention relates to an apparatus installed in a receiver for data transmission for compensating for phase hits which occur on a transmission channel to invite transmission errors.
In a phase hit compensating apparatus of the kind described, it has been customary to extract a carrier phase from a received signal and rotate the phase of the received signal so as to control the carrier phase to zero. A problem with this prior art control, generally referred to as a feedback control, is that upon occurrence of a phase hit of .chi. degrees the amount of phase rotation which should follow the phase hit cannot reach the .chi. degrees without a certain time constant, i.e., until a certain period of time expires. Hence, although the influence of such a phase hit may eventually be reduced to zero, it does affect the reception of data immediately after the occurrence of the phase hit. Especially, this problem is of cardinal importance when it comes to a phase modulation (PHM) type and a quadrature amplitude modulation (QAM) type receiver because, in these receivers, the increase of the phase hit angle over a certain limit causes transmission errors to occur all of a sudden.